The present disclosure relates generally to detection of reinforcement metal corrosion. More particularly, the present disclosure pertains to systems, devices, and methods for use in detection of corrosion, conditions for corrosion, and/or conditions favorable for corrosion of reinforcement metal (e.g., steel reinforcement within concrete structures, etc.).
A large part of civil infrastructure includes concrete reinforced with steel (“reinforced concrete”). The steel in reinforced concrete may be subject to corrosion, which is a factor in the premature deterioration of civil structures. Damage due to corrosion may reduce the service life of the infrastructure and may create safety hazards.
Ingress of Chloride (Cl—) ions into concrete is a cause of corrosion damage. When a structure is first built, bare reinforcement steel is often exposed to oxygen and water and a very thin (approximately 1 micrometer (μm)) dense layer of either metal oxide or hydroxide may be formed on the surface forming a thin passive layer. The reinforcement steel (e.g., steel bars or rods) may be protected from corrosion by this thin passive layer. Further, the highly alkaline environment of the surrounding concrete (e.g., pH value of about 12.6) may help maintain the thin passive layer on the surface of the reinforcement steel.
However, Chloride (Cl—) ions from de-icing salts often used to keep roads clear of snow and ice and from exposure to marine environment or admixtures (e.g., present at the time of concrete mixing) may permeate the concrete to reach the reinforcement steel (e.g., located at a depth below a surface of the concrete) and destroy the thin passive layer. After the thin passive layer is destroyed, corrosion of the reinforcement steel may begin.
Once corrosion begins, corrosion is self-sustaining. Rust formation (e.g., which is a corrosion product) on the outer surface of the reinforcement steel may result in an increase in the size (e.g., the cross-sectional size) of the reinforcement steel. For example, rust occupies about two to about six times the volume of original reinforcement steel, and as a result, the rust may exert stress within the concrete that cannot be supported by its limited plastic deformation. This stress may generate cracks and spalls, which subsequently may lead to the degradation of the structure and may provide new means for water and Cl— ions to reach the reinforcement steel.
Since reinforcement steel is embedded in concrete, by the time the effects of corrosion are visible on the surface of the concrete, the damage to the concrete may be severe. The estimated cost of repairing reinforced concrete structures may be greater than about $200 per square meter of exposed, damaged surface. As a result, repair, maintenance, and replacement cost of reinforced concrete often consumes a substantial amount of public spending on civil infrastructure. Further, reinforcement steel corrosion is not just an economic issue. Due to the corrosion of reinforcement steel, concrete structures may collapse potentially harming people.
Early detection of reinforcement steel corrosion may involve destructive testing of a suspected area of corrosion. However, certain nondestructive evaluation (NDE) methods and technologies exist for early detection of reinforcement steel corrosion. Most existing NDE sensing technology used for monitoring corrosion utilize a wired connection from an embedded sensor in the concrete to outside of the concrete. The installation and preparation of wired sensors for monitoring corrosion is often expensive and time consuming.
Another NDE sensing technology for early detection of corrosion of reinforcement steel utilizes embeddable wireless corrosion sensors (see, e.g., M. M. Andring a, D. P. Neikirk, N. P. Dickerson and S. L. Wood, “Unpowered wireless corrosion sensor for steel reinforced concrete,” in Proc. IEEE Sensors, 2005, pp. 155-158; and P. P. Pasupathy, M. Zhuzhou, D. P. Neikirk and S. L. Wood, “Unpowered resonant wireless sensor nets for structural health monitoring,” in Proc. IEEE Sensors, 2008, pp. 697-700). For example, several wireless embeddable corrosion sensors are commercially available such as, e.g., the ECI by Virginia Technologies, Inc. (see, e.g., “Embedded Corrosion Instrument,”[Online]. Available: http://www.vatechnologies.com/eciNeed.htm. [Accessed: Oct. 5, 2009]) and the concrete corrosion sensor by RocTest (see, e.g., “Concrete Corrosion sensor,” [online]. Available: http://www.roctest.com/modules/AxialRealisation/img_repository/files/documents/SensCore-161010.pdf. [Accessed: Jan. 16, 2010]).
Such wireless corrosion sensors, however, often require a local power source (e.g., a battery) for electronics in the sensor, which may negate an advantage of using a wireless sensor because the local power source may require frequent recharging or replacement. Further, wireless corrosion sensors are often expensive.
The tendency of reinforcement steel to corrode in concrete may be indicated by a potential it develops in contact with the concrete environment, which may be referred to as “corrosion potential.” Corrosion potential can provide information for corrosion probability and may be affected by a number of factors, which include polarization by limited diffusion of oxygen, concrete porosity, and the presence of a highly resistive layer. One wired NDE method available for corrosion monitoring, open circuit potential measurement, measures the corrosion potential of reinforcement steel with respect to a reference electrode (see, e.g., H. Song and V. Saraswathy, “Corrosion monitoring of reinforced concrete structures—a review,” International Journal of Electrochemical Science, vol. 2, pp. 1-28, January 2007).